Preparation method of phosphorus pentafluoride

Abstract

The invention relates to a preparation method of phosphorus pentafluoride, and belongs to the technical field of inorganic chemical production. Polyphosphoric acid, anhydrous hydrofluoric acid and sulfur trioxide are used as reaction raw materials, concentrated sulfuric acid is used as a priming solution and a complexing agent, and the phosphorus pentafluoride gas is prepared by a one-step method. According to the one-step method for preparing the phosphorus pentafluoride, the problems that in the traditional two-step method for preparing the phosphorus pentafluoride, an intermediate product hexafluorophosphoric acid is prone to hydrolysis, and the product is difficult to purify are solved, the reaction efficiency is effectively improved, and the purity of the product is improved. Furthermore, aiming at the characteristics of preparing phosphorus pentafluoride by a one-step method, the invention specifically develops a double-reactor circulating switching reaction, so that the reaction raw material hydrofluoric acid in the system can be recycled, the reaction efficiency is improved on the premise of ensuring that the hydrofluoric acid material is excessive, and meanwhile, the separation of phosphorus pentafluoride and hydrogen fluoride mixed gas after the reaction is realized; the purity of the phosphorus pentafluoride gas is improved, and the purification difficulty of the crude phosphorus pentafluoride gas is reduced.

Description

Technical Field

[0001] The invention relates to a method for preparing phosphorus pentafluoride, and belongs to the technical field of inorganic chemical production. Background Art

[0002] Phosphorus pentafluoride (PF5) is an important phosphorus-halogen compound. It is a colorless, pungent, foul-smelling gas at room temperature and pressure. It is highly irritating to the skin, eyes, and mucous membranes. Phosphorus pentafluoride is a highly active compound that will hydrolyze violently in humid air to produce toxic and corrosive white hydrogen fluoride smoke. Phosphorus pentafluoride is widely used in industry. For example, in the electronics industry, phosphorus pentafluoride is an N-type doping source for silicon epitaxy, diffusion, and ion implantation processes, effectively improving semiconductor performance; in the field of polymer materials, phosphorus pentafluoride is a raw material for synthesizing fluorinated organic dithiophosphates, terephthalate, and other polymers; in the field of catalysis, phosphorus pentafluoride is a catalyst for polymerization, hydrocarbonization, dehydrogenation, and hydrocarbon cracking reactions. Titanium, nickel, beryllium, and other metal oxides treated with phosphorus pentafluoride as catalysts can improve reaction selectivity. In addition, phosphorus pentafluoride can also be used to synthesize fine chemicals such as herbicides.

[0003] In recent years, with the increasingly serious environmental problems, the gradual depletion of fossil energy such as oil and coal, as well as the widespread use of electric vehicles and the rapid development of electronic products, the lithium battery market has grown dramatically, and phosphorus pentafluoride, as an important production raw material for lithium hexafluorophosphate (LiPF6), the electrolyte of lithium batteries, has also seen a rapid increase in market demand. Therefore, at this stage, phosphorus pentafluoride preparation technology and product quality improvement have become the focus of research and attention in related industries in China.

[0004] At present, there are many methods for preparing phosphorus pentafluoride, which can be mainly divided into two categories: direct method and indirect method. Among them, the direct method is to prepare phosphorus pentafluoride by direct reaction of phosphorus source and hydrogen fluoride. The most widely used and mature method in industrial application is to use phosphorus pentachloride as a phosphorus source and directly react with hydrogen fluoride to prepare phosphorus pentafluoride. However, the reaction is highly exothermic and difficult to control. In addition, PCl5 is easy to volatilize and cause pipeline blockage, and the by-product hydrogen chloride (HCl) and PF5 have similar boiling points and require high separation energy consumption. The indirect method refers to a method in which the reactants first generate intermediate products (phosphorus oxytrifluoride (POF3), hexafluorophosphoric acid (HPF6), etc.), and then the intermediate products are treated to obtain phosphorus pentafluoride.

[0005] The Chinese invention patent application with a publication date of March 14, 2023 and a publication number of CN115784182A discloses a method for preparing phosphorus pentafluoride, comprising the following steps: (1) introducing nitrogen into a reactor for displacement, and then introducing polyphosphoric acid and anhydrous hydrogen fluoride, the reaction temperature is between 10 and 0°C, and the reaction time is 2 to 5 hours; (2) slowly introducing fuming sulfuric acid into the reactor for dehydration, and then introducing the product into a heating decomposition reactor for heating and decomposition to generate phosphorus pentafluoride gas. The preparation method uses the decomposition intermediate hexafluorophosphoric acid to produce phosphorus pentafluoride, and adds fuming sulfuric acid or other dehydrating agents during the reaction process, does not produce a large amount of water, and the yield of phosphorus pentafluoride is greater than 95%. However, the reaction process of the preparation method is long, and the low-temperature reaction efficiency of the first step is low, and hexafluorophosphoric acid is easily hydrolyzed, which makes it more difficult to purify phosphorus pentafluoride gas and increases the process energy consumption.

[0006] A Chinese invention patent application with a publication date of December 26, 2023 and a publication number of CN117285021A discloses a method for preparing phosphorus pentafluoride gas, comprising the following steps: (1) reacting a phosphorus-containing compound with hydrogen fluoride and an organic anhydride dehydrating agent to generate a hexafluorophosphoric acid solution; (2) heating the hexafluorophosphoric acid solution to decompose it into gaseous hydrogen fluoride and phosphorus pentafluoride. This preparation method reacts a phosphorus-containing compound, hydrogen fluoride and an organic anhydride dehydrating agent to generate a hexafluorophosphoric acid solution. The reaction heat effect is smaller than that of SO3, the reaction is easy to control, and the reaction and dehydration can be carried out simultaneously, thereby improving production efficiency. However, this reaction is the same as the above-mentioned patent, and both are two-step methods for preparing phosphorus pentafluoride. In order to reduce the occurrence of hexafluorophosphoric acid hydrolysis reaction, the first step of the synthesis reaction needs to be carried out under low temperature conditions, which is easy to cause incomplete reaction and too long reaction time, thereby affecting the purity and yield of phosphorus pentafluoride. Summary of the invention

[0007] The purpose of the present invention is to provide a method for preparing phosphorus pentafluoride to solve the problem that hexafluorophosphoric acid is easily hydrolyzed and the reaction efficiency is low when phosphorus pentafluoride is prepared by an indirect method in the prior art.

[0008] In order to achieve the above object, a technical solution of a method for preparing phosphorus pentafluoride in the present invention is: A method for preparing phosphorus pentafluoride comprises the following steps: concentrated sulfuric acid and polyphosphoric acid are mixed to obtain a reaction base liquid; the reaction base liquid is reacted with anhydrous hydrofluoric acid and sulfur trioxide liquid at 125-145° C. under a protective atmosphere to obtain crude phosphorus pentafluoride gas.

[0009] The beneficial effect of the above technical scheme is that the preparation method of phosphorus pentafluoride of the present invention is a pioneering invention. The present invention uses polyphosphoric acid, anhydrous hydrofluoric acid and sulfur trioxide as reaction raw materials, and uses concentrated sulfuric acid as a base solution and a complexing agent to prepare phosphorus pentafluoride gas in a one-step method. The one-step method of the present invention prepares phosphorus pentafluoride, by controlling a substantially anhydrous reaction system, solves the problem that the intermediate product hexafluorophosphoric acid is easily hydrolyzed, has a low yield, and is difficult to purify the product in the traditional two-step method for preparing phosphorus pentafluoride, effectively improves the efficiency of the reaction, and improves the purity of the product.

[0010] Furthermore, the present invention adopts concentrated sulfuric acid as the base solution, which can significantly enhance the fluidity of polyphosphoric acid, increase the volume of the reaction base liquid, make the entire reaction more complete, and improve the efficiency of the reaction; and the concentrated sulfuric acid can complex the excess hydrogen fluoride and sulfur trioxide gas in the reaction raw materials to achieve the effect of preliminary purification of phosphorus pentafluoride, further improve the purity of phosphorus pentafluoride gas, and simplify the subsequent purification process.

[0011] Specifically, the concentration of concentrated sulfuric acid is ≥98%.

[0012] As a further improvement, the crude phosphorus pentafluoride gas is introduced into the reaction base liquid for purification to obtain a hydrofluoric acid-enriched liquid and purified phosphorus pentafluoride gas.

[0013] The beneficial effect of the above technical solution is that the crude phosphorus pentafluoride gas generated by the reaction is introduced into the reaction base liquid, and the concentrated sulfuric acid can complex the excess hydrogen fluoride and sulfur trioxide gas to preliminarily purify the phosphorus pentafluoride gas, which is beneficial to improve the purity of the product and simplify the subsequent further purification process.

[0014] As a further improvement, anhydrous hydrofluoric acid and sulfur trioxide liquid are added to the hydrofluoric acid-enriched liquid to carry out the reaction to prepare crude phosphorus pentafluoride gas.

[0015] The beneficial effect of the above technical solution is that the purified hydrofluoric acid-enriched liquid is supplemented with anhydrous hydrofluoric acid and sulfur trioxide liquid to prepare phosphorus pentafluoride gas, thereby achieving the effect of fully utilizing the reaction raw materials.

[0016] As a further improvement, the reaction is a dual-reactor cyclic switching reaction; the reactor comprises a reactor 1 and a reactor 2 connected in series; the dual-reactor cyclic switching reaction comprises the following steps: (1) adding anhydrous hydrofluoric acid and sulfur trioxide liquid into a reactor 1 containing a reaction base liquid to react and obtain crude phosphorus pentafluoride gas, and passing the crude phosphorus pentafluoride gas into a reactor 2 containing a reaction base liquid for purification to obtain purified phosphorus pentafluoride gas; (2) After the reaction in reactor 1 is completed, the connection between reactor 1 and reactor 2 is cut off, the liquid generated in reactor 1 is discharged and the reaction base liquid is added; After purification, anhydrous hydrofluoric acid and sulfur trioxide liquid are added to the reactor 2 to react and obtain crude phosphorus pentafluoride gas, and the crude phosphorus pentafluoride gas is passed into the reactor 1 containing the reaction base liquid for purification to obtain purified phosphorus pentafluoride gas; (3) After the reaction in reactor 2 is completed, the connection between reactor 1 and reactor 2 is cut off, the liquid generated in reactor 2 is discharged and the reaction base liquid is added; (4) Steps (1) to (3) are repeated in a cycle.

[0017] The beneficial effect of the above technical solution is that: further, the present invention develops a dual-reactor cyclic switching reaction specifically for the characteristics of preparing phosphorus pentafluoride by a one-step method, which can recycle the hydrofluoric acid as a reaction raw material in the system, improve the reaction efficiency under the premise of ensuring excess hydrofluoric acid material, and at the same time realize the separation of phosphorus pentafluoride and hydrogen fluoride mixed gas after the reaction, improve the purity of phosphorus pentafluoride gas, and reduce the difficulty of purifying crude phosphorus pentafluoride gas.

[0018] Furthermore, the dual-reactor cyclic switching reaction can make the entire reaction process uninterrupted and continuous, which helps to improve the efficiency of industrial production and further reduce production costs. In addition, part of the concentrated sulfuric acid solution used as the base solution in the reaction process is recycled with the mixed solution of polyphosphoric acid, and the other part is used in the fluorite method to prepare anhydrous hydrogen fluoride or sold.

[0019] As a further improvement, the purified phosphorus pentafluoride gas is subjected to distillation treatment to obtain high-purity phosphorus pentafluoride gas.

[0020] As a further improvement, the temperature of the distillation treatment is -20~10°C and the pressure is 50~100Kpa.

[0021] As a further improvement, the mass ratio of the concentrated sulfuric acid to the polyphosphoric acid is (1-3):1.

[0022] As a further improvement, the molar ratio of phosphorus in the polyphosphoric acid to fluorine in anhydrous hydrofluoric acid is 1:(6-9).

[0023] As a further improvement, the molar ratio of phosphorus in the polyphosphoric acid to sulfur in sulfur trioxide is 1:(3.3-4). BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a process flow chart of the method for preparing phosphorus pentafluoride in Example 1 of the present invention. DETAILED DESCRIPTION

[0025] In the prior art, when phosphorus pentafluoride is prepared by an indirect method, most of them use a two-step method. However, the following problems exist when phosphorus pentafluoride is prepared by a two-step method: ① The synthesis reaction of the intermediate product hexafluorophosphoric acid generates water, which is prone to hydrolysis of hexafluorophosphoric acid, resulting in low purity of hexafluorophosphoric acid, and many side reactions (hydrolysis reactions), making subsequent purification of phosphorus pentafluoride difficult; ② In order to reduce the occurrence of hexafluorophosphoric acid hydrolysis reaction, the synthesis of hexafluorophosphoric acid must be carried out at a low temperature, resulting in incomplete reaction and long reaction time. Based on this, the present invention provides a method for preparing phosphorus pentafluoride.

[0026] The present invention uses polyphosphoric acid, anhydrous hydrofluoric acid and sulfur trioxide as reaction raw materials, and uses concentrated sulfuric acid as a base solution and a complexing agent to prepare phosphorus pentafluoride gas in a one-step method. The reaction equation involved in the one-step method for preparing phosphorus pentafluoride in the present invention is: H n+2 P n O 3n+1 + 5nHF + (3n+1)SO3→nPF5+ (3n+1)H2SO4.

[0027] The invention solves the problem that the intermediate product hexafluorophosphoric acid is prone to hydrolysis and the product purification is difficult in the traditional two-step method for preparing phosphorus pentafluoride by controlling a substantially anhydrous reaction system, thereby effectively improving the reaction efficiency and the purity of the product.

[0028] Moreover, in order to improve the reaction efficiency and simplify the subsequent purification process, the crude phosphorus pentafluoride gas generated by the reaction can be introduced into the reaction base liquid for purification, and the hydrogen fluoride and sulfur trioxide gas therein are complexed to achieve the preliminary purification of the crude phosphorus pentafluoride gas, simplifying the subsequent purification process. The purified reaction base liquid is supplemented with anhydrous hydrofluoric acid and sulfur trioxide liquid to continue the preparation process of phosphorus pentafluoride gas, without waste of reaction raw materials, and improving the efficiency of the reaction.

[0029] Furthermore, in order to improve the reaction efficiency under the premise of ensuring the excess of hydrofluoric acid material, the separation of phosphorus pentafluoride and hydrogen fluoride mixed gas after the reaction is achieved, and the difficulty of purifying crude phosphorus pentafluoride gas is reduced. The present invention also provides a dual-reactor cyclic switching reaction, which can make the entire reaction process uninterrupted and continuous, help to improve the efficiency of industrial production, and further reduce production costs.

[0030] To further describe the present invention, it should be noted that, under the premise of no conflict, the embodiments or technical features described below can be arbitrarily combined to form new embodiments. The equipment and raw materials used can be purchased from the market or are commonly used in the art. The methods in the following embodiments are all conventional methods in the art unless otherwise specified.

[0031] A specific embodiment of a method for preparing phosphorus pentafluoride of the present invention: Example 1 The reaction equation involved in the preparation method of phosphorus pentafluoride in this embodiment is: H6P4O 13 + 20HF +13SO3→4 PF5↑+ 13H2SO4; the preparation process is as follows Figure 1 As shown in , the following steps are included: (1) Mix 100 kg of concentrated sulfuric acid and 100 kg of polyphosphoric acid (H6P4O 13 ) and mix well to obtain a reaction base liquid.

[0032] (2) Nitrogen was introduced into the reaction system to replace the air in the reaction system, and then 100 kg of the reaction base liquid obtained in step (1) was added to reactor #1 and reactor #2, respectively.

[0033] Into the No. 1 reactor, 71.01 kg of anhydrous hydrofluoric acid and 156.21 kg of sulfur trioxide liquid were simultaneously introduced for reaction. The reaction temperature was controlled at 125°C and the reaction time was 1 hour. The phosphorus pentafluoride and excess hydrogen fluoride and sulfur trioxide mixed gas generated by the reaction were introduced into the No. 2 reactor. After the hydrogen fluoride and sulfur trioxide were removed through the reaction, crude phosphorus pentafluoride gas was obtained.

[0034] After the reaction in reactor #1 is completed (the reaction is complete when no gas escapes), the connection between reactor #1 and reactor #2 is cut off, the sulfuric acid solution in reactor #1 is discharged and new reaction base liquid is added.

[0035] 71.01 kg of anhydrous hydrofluoric acid and 156.21 kg of sulfur trioxide liquid were simultaneously introduced into the 2# reactor for reaction. The reaction temperature was controlled at 125°C and the reaction time was 1 hour. After the reaction was completed, the mixed gas of phosphorus pentafluoride, hydrogen fluoride and sulfur trioxide generated was introduced into the 1# reactor. After the hydrogen fluoride and sulfur trioxide were removed through the reaction, crude phosphorus pentafluoride gas was obtained.

[0036] After the reaction in the 2# reactor is completed, the connection between the 1# reactor and the 2# reactor is cut off, the sulfuric acid solution in the 2# reactor is discharged and a new reaction base liquid is added.

[0037] In this cycle, the 1# reactor and the 2# reactor are switched in a cycle according to this process method, thereby realizing the recycling of the anhydrous hydrogen fluoride gas in the system.

[0038] (3) The crude phosphorus pentafluoride gas discharged from the 1# reactor and the 2# reactor was introduced into a distillation tower. The distillation temperature was controlled at 10°C and the pressure was 100 KPa. After distillation, 144.66 kg of high-purity phosphorus pentafluoride gas was obtained with a purity of 99.98% and a yield of 97.02%.

[0039] Part of the sulfuric acid solution discharged from the 1# reactor and the 2# reactor is mixed with polyphosphoric acid to prepare a mixed solution for recycling, and the other part is used in the fluorite method for preparing anhydrous hydrogen fluoride or sold.

[0040] The reaction of this embodiment is essentially to pass the gas generated by the 1# reactor into a reaction base liquid composed of concentrated sulfuric acid and polyphosphoric acid for purification and absorption and then discharge to obtain crude phosphorus pentafluoride gas. The purification and absorption process of the reaction base liquid not only realizes the recovery of HF, SO3, etc., but also reduces the difficulty of subsequent distillation and separation of phosphorus pentafluoride, thereby being conducive to obtaining phosphorus pentafluoride gas with higher purity and yield. In the yield calculation, the theoretical mass of its phosphorus pentafluoride gas is calculated based on the amount of polyphosphoric acid in the 1# reactor. After the gas generated by the 1# reactor is purified and distilled by the reaction base liquid, the actual output of the phosphorus pentafluoride gas in the 1# reactor is counted, and then the yield is calculated based on the ratio of the actual output to the theoretical output.

[0041] Example 2 The reaction equation involved in the preparation method of phosphorus pentafluoride in this embodiment is: H6P4O 13 + 20HF +13SO3→4 PF5↑+ 13H2SO4; The preparation method comprises the following steps: (1) Mix 200 kg of concentrated sulfuric acid and 100 kg of polyphosphoric acid (H6P4O 13 ) and mix well to obtain a reaction base liquid.

[0042] (2) Nitrogen was introduced into the reaction system to replace the air in the reaction system, and then 150 kg of the reaction base liquid obtained in step (1) was added to reactor #1 and reactor #2, respectively.

[0043] Into the No. 1 reactor, 88.76 kg of anhydrous hydrofluoric acid and 165.68 kg of sulfur trioxide liquid were simultaneously introduced for reaction. The reaction temperature was controlled at 135° C. and the reaction time was 40 min. The phosphorus pentafluoride generated by the reaction and the excess hydrogen fluoride and sulfur trioxide mixed gas were introduced into the No. 2 reactor. After the hydrogen fluoride and sulfur trioxide were removed through the reaction, crude phosphorus pentafluoride gas was obtained.

[0044] After the reaction in reactor #1 is completed (the reaction is complete when no gas escapes), the connection between reactor #1 and reactor #2 is cut off, the sulfuric acid solution in reactor #1 is discharged and new reaction base liquid is added.

[0045] 88.76 kg of anhydrous hydrofluoric acid and 165.68 kg of sulfur trioxide liquid were simultaneously introduced into the No. 2 reactor for reaction. The reaction temperature was controlled at 135°C and the reaction time was 40 min. After the reaction was completed, the mixed gas of phosphorus pentafluoride, hydrogen fluoride and sulfur trioxide generated was introduced into the No. 1 reactor. After the hydrogen fluoride and sulfur trioxide were removed through the reaction, crude phosphorus pentafluoride gas was obtained.

[0046] After the reaction in the 2# reactor is completed, the connection between the 1# reactor and the 2# reactor is cut off, the sulfuric acid solution in the 2# reactor is discharged and a new reaction base liquid is added.

[0047] In this cycle, the 1# reactor and the 2# reactor are switched in a cycle according to this process method, thereby realizing the recycling of the anhydrous hydrogen fluoride gas in the system.

[0048] (3) The crude phosphorus pentafluoride gas discharged from the 1# reactor and the 2# reactor was introduced into a distillation tower. The distillation temperature was controlled at -20°C and the pressure was 50 KPa. After distillation, 145.55 kg of high-purity phosphorus pentafluoride gas was obtained with a purity of 99.99% and a yield of 97.61%.

[0049] Part of the sulfuric acid solution discharged from the 1# reactor and the 2# reactor is mixed with polyphosphoric acid to prepare a mixed solution for recycling, and the other part is used in the fluorite method for preparing anhydrous hydrogen fluoride or sold.

[0050] Example 3 The reaction equation involved in the preparation method of phosphorus pentafluoride in this embodiment is: H6P4O 13 + 20HF +13SO3→4 PF5↑+ 13H2SO4; The preparation method comprises the following steps: (1) Mix 300 kg of concentrated sulfuric acid and 100 kg of polyphosphoric acid (H6P4O 13 ) and mix well to obtain a reaction base liquid.

[0051] (2) Nitrogen was introduced into the reaction system to replace the air in the reaction system, and then 200 kg of the reaction base liquid obtained in step (1) was added to reactor #1 and reactor #2, respectively.

[0052] Into the No. 1 reactor, 106.51 kg of anhydrous hydrofluoric acid and 189.34 kg of sulfur trioxide liquid were simultaneously introduced for reaction. The reaction temperature was controlled at 145°C and the reaction time was 0.5 h. The phosphorus pentafluoride and excess hydrogen fluoride and sulfur trioxide mixed gas generated by the reaction were introduced into the No. 2 reactor. After the hydrogen fluoride and sulfur trioxide were removed through the reaction, crude phosphorus pentafluoride gas was obtained.

[0053] After the reaction in reactor #1 is completed (the reaction is complete when no gas escapes), the connection between reactor #1 and reactor #2 is cut off, the sulfuric acid solution in reactor #1 is discharged and new reaction base liquid is added.

[0054] 106.51 kg of anhydrous hydrofluoric acid and 189.34 kg of liquid sulfur trioxide were simultaneously introduced into the No. 2 reactor for reaction. The reaction temperature was controlled at 145°C and the reaction time was 0.5 h. After the reaction was completed, the mixed gas of phosphorus pentafluoride, hydrogen fluoride and sulfur trioxide generated was introduced into the No. 1 reactor. After the hydrogen fluoride and sulfur trioxide were removed through the reaction, crude phosphorus pentafluoride gas was obtained.

[0055] After the reaction in the 2# reactor is completed, the connection between the 1# reactor and the 2# reactor is cut off, the sulfuric acid solution in the 2# reactor is discharged and a new reaction base liquid is added.

[0056] In this cycle, the 1# reactor and the 2# reactor are switched in a cycle according to this process method, thereby realizing the recycling of the anhydrous hydrogen fluoride gas in the system.

[0057] (3) The crude phosphorus pentafluoride gas discharged from the 1# reactor and the 2# reactor was introduced into a distillation tower. The distillation temperature was controlled at -10°C and the pressure was 100 KPa. After distillation, 144.15 kg of high-purity phosphorus pentafluoride gas was obtained with a purity of 99.98% and a yield of 98.01%.

[0058] Part of the sulfuric acid solution discharged from the 1# reactor and the 2# reactor is mixed with polyphosphoric acid to prepare a mixed solution for recycling, and the other part is used in the fluorite method for preparing anhydrous hydrogen fluoride or sold.

[0059] Example 4 The reaction equation involved in the preparation method of phosphorus pentafluoride in this embodiment is: H6P4O 13 + 20HF +13SO3→4 PF5↑+ 13H2SO4; The preparation method comprises the following steps: (1) Mix 300 kg of concentrated sulfuric acid and 100 kg of polyphosphoric acid (H6P4O 13 ) and mix well to obtain a reaction base liquid.

[0060] (2) Nitrogen is introduced into the reaction system to replace the air in the reaction system, and then the reaction base liquid obtained in step (1) is added to the reactor.

[0061] 142.01 kg of anhydrous hydrofluoric acid and 312.43 kg of sulfur trioxide liquid were simultaneously introduced into the reactor for reaction. The reaction temperature was controlled at 125°C and the reaction time was 1 hour. The phosphorus pentafluoride generated by the reaction and the excess hydrogen fluoride and sulfur trioxide mixed gas were introduced into the distillation tower. The distillation temperature was controlled at -10°C and the pressure was 100 KPa. After distillation, 145.05 kg of high-purity phosphorus pentafluoride gas was obtained with a purity of 98.57% and a yield of 97.28%.

[0062] Part of the sulfuric acid solution discharged from the reactor is mixed with polyphosphoric acid to prepare a mixed solution for recycling, and the other part is used in the fluorite method for preparing anhydrous hydrogen fluoride or sold.

[0063] In summary, the phosphorus pentafluoride prepared by the one-step method in Example 4 has a high purity and yield, and the product meets the needs of high-end application fields such as new energy. Further, the present invention develops a dual-reactor cyclic switching reaction mode (as described in Examples 1 to 3), and uses a one-step method to prepare phosphorus pentafluoride, which can recycle the reaction raw material hydrofluoric acid in the system, improve the efficiency of the reaction while ensuring the excess of hydrofluoric acid material, and further improve the purity and yield of phosphorus pentafluoride gas.

[0064] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. The patent protection scope of the present invention shall be based on the claims. All equivalent structural changes made using the contents of the specification of the present invention should also be included in the protection scope of the present invention.

Claims

1. A method for preparing phosphorus pentafluoride, characterized in that: The following steps are involved: Concentrated sulfuric acid and polyphosphoric acid are mixed to obtain a reaction base liquid, and the reaction base liquid is reacted with anhydrous hydrofluoric acid and sulfur trioxide liquid at 125-145° C. under a protective atmosphere to obtain crude phosphorus pentafluoride gas.

2. The method for preparing phosphorus pentafluoride according to claim 1, characterized in that: The crude phosphorus pentafluoride gas is introduced into the reaction base liquid for purification to obtain a liquid enriched with hydrofluoric acid and purified phosphorus pentafluoride gas.

3. The method for preparing phosphorus pentafluoride according to claim 2, characterized in that: Anhydrous hydrofluoric acid and sulfur trioxide liquid are added to the hydrofluoric acid-enriched liquid to carry out the reaction to prepare crude phosphorus pentafluoride gas.

4. The method for preparing phosphorus pentafluoride according to claim 1, characterized in that: The reaction is a dual-reactor cyclic switching reaction; the reactor comprises a reactor 1 and a reactor 2 connected in series; the dual-reactor cyclic switching reaction comprises the following steps: (1) adding anhydrous hydrofluoric acid and sulfur trioxide liquid into a reactor 1 containing a reaction base liquid to react and obtain crude phosphorus pentafluoride gas, and passing the crude phosphorus pentafluoride gas into a reactor 2 containing a reaction base liquid for purification to obtain purified phosphorus pentafluoride gas; (2) After the reaction in reactor 1 is completed, the connection between reactor 1 and reactor 2 is cut off, the liquid generated in reactor 1 is discharged and new reaction base liquid is added; After purification, anhydrous hydrofluoric acid and sulfur trioxide liquid are added to the reactor 2 to react and obtain crude phosphorus pentafluoride gas, and the crude phosphorus pentafluoride gas is passed into the reactor 1 containing the reaction base liquid for purification to obtain purified phosphorus pentafluoride gas; (3) After the reaction in reactor 2 is completed, the connection between reactor 1 and reactor 2 is cut off, the liquid generated in reactor 2 is discharged and the reaction base liquid is added; (4) Steps (1) to (3) are repeated in a cycle.

5. The method for preparing phosphorus pentafluoride according to any one of claims 2 to 4, characterized in that: The purified phosphorus pentafluoride gas is subjected to rectification treatment to obtain high-purity phosphorus pentafluoride gas.

6. The method for preparing phosphorus pentafluoride according to claim 5, characterized in that: The temperature of the distillation treatment is -20~10°C and the pressure is 50~100Kpa.

7. The method for preparing phosphorus pentafluoride according to any one of claims 1 to 4, characterized in that: The mass ratio of the concentrated sulfuric acid to the polyphosphoric acid is (1-3):

1.

8. The method for preparing phosphorus pentafluoride according to any one of claims 1 to 4, characterized in that: The molar ratio of phosphorus in the polyphosphoric acid to fluorine in the anhydrous hydrofluoric acid is 1:(6-9).

9. The method for preparing phosphorus pentafluoride according to any one of claims 1 to 4, characterized in that: The molar ratio of phosphorus in the polyphosphoric acid to sulfur in sulfur trioxide is 1:(3.3-4).

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